1. Field of the Invention
The present invention relates to a method for producing polyorganosiloxane using a solid, acidic zirconium oxide catalyst, more particularly a method for producing a polyorganosiloxane from at least one type of organosilicon compound having a siloxane unit or alkoxysilane as a starting material in the presence of an acidic catalyst, wherein a solid, acidic zirconium oxide catalyst is used as the acidic catalyst to produce the polyorganosiloxane by the equilibrating reaction involving cleavage and recombination of the silicon-oxygen bond.
2. Description of the Prior Art
Polyorganosiloxane has been widely used in the chemical industry because of its high resistance to heat, cold weather and radioactive ray, excellent electrical characteristics, and peculiar interfacial characteristics, e.g., low surface tension. Polymerization for producing polyorganosiloxane is generally based on an equilibrating reaction involving cleavage/recombination of a siloxane chain present in a cyclic polyorganosiloxane, low-molecular-weight linear polyorganosiloxane or organoalkoxysilane in the presence of an acidic or basic catalyst, or hydrolysis and subsequent dehydration/condensation of dichloroorganosilane, dialkoxydiorganosilane or the like.
In particular, an equilibrating reaction has been extensively employed because of low hazardousness of the starting material and easiness of controlling polymerization degree of the product. This reaction has been widely used for various purposes, e.g., for reducing polymerization degree of polyorganosiloxane and introduction of a functional group, in addition to polymerization. For example, the equilibrating reaction between polydimethylsiloxane and hexamethyldisiloxane can realize low polymerization degree. It can make cyclic polyorganosiloxane, when controlled at an elevated temperature and vacuum. Moreover, the equilibrating reaction between, e.g., a hydrolysis/condensation product of N-β-(aminoethyl)-γ-aminopropylmethyldimethoxysilane and dimethylpolysiloxane in the presence of an alkali catalyst can produce an amino-modified polysiloxane.
A number of materials have been proposed as the catalysts for the above-described equilibrating reactions. They include those based on sulfuric acid, hydrochloric acid, a Lewis acid, sodium hydroxide, potassium hydroxide, tetramethyl ammonium hydroxide, butyl phosphonium silanolate, an amine and phosphonitrile halide. However, these catalysts are not highly efficient, because they need a neutralization step and removal of the neutralization product for catalyst inactivation and removal. Moreover, the recovered neutralization product is difficult to recycle, because of its incompatibility with a filtration aid, polysiloxane or the like, and is at present disposed by incineration or land filling.
The production processes which can replace the present processes, which massively discharge wastes, are increasing in the midst of the heightened requirements for environmental protection. In particular, use of an acidic catalyst is essential for production of polyorganosiloxane, which contains the ≡Si—H bond, because the bond is undesirably reactive in the presence of an alkali catalyst. An acidic catalyst should be incorporated at as high as 1 to 5 parts by volume per 100 parts by volume of the starting material to secure a practical reaction rate. Therefore, it involves a disadvantage of massively discharging wastes.
Moreover, these acidic catalysts are very corrosive to metals, and the system needs expensive materials corrosion-resistant or lined.
Recently, polyorganosiloxanes have been going into materials for electronic devices or the like, which need highly refined starting materials. However, the polyorganosiloxanes produced in the presence of a conventional catalyst tend to have limited applications, because of trace quantities of the catalyst, neutralization product, neutralizer or the like remaining in the product.
Solid, acidic catalysts, e.g., zeolite, ion-exchanging resin, acid-activated acidic clay, have been proposed. However, few conventional acidic catalysts have been massively used, because of the reaction rate being impractically low over them.